I grew up in a small town in the hard rock mining area of No. California. Every spring there would be a cave in somwhere (usually under the football field of the Junior High). A hole would open up 10-15 ft. wide and 8 ft. deep. They just filled it in and went on. I can't imagine a hole opening up into a huge depth of a 2000 degree fiery pit. And yes, I suppose it could follow a seam to the next town. Wouldn't even have to have been mined. That fire could be on the border of Kansas for a possiblity.